What is the best way to isolate a CAN interface in industrial applications where the highest speed (512kbps or 1Mbps) is required and what is the best distance to achieve at that baud rate?
Methods of isolation that exists today includes optical isolation, capacitive isolation and inductive isolation. Optical isolation is the more traditional way of implementing isolation, but recently new developments in digital isolation using inductive coupling in the form of transformers have been able to meet the isolation specifications of optical isolation.
We use inductive isolation with our iCoupler technology and integrated this technology with our CAN transceiver technology to create isolated CAN products, the ADM3053 and ADM3052.
The ADM3053 is the smallest product on the market available today that includes both signal and power isolation and a CAN transceiver.The ADM3052 is a signal isolated CAN transceiver with an integrated linear bus side voltage regulator for bus powered applications at 24V.
The ADM3053 typically gets used in CANOpen applications which allows for cable lengths of up to 25m at 1Mbps. The ADM3052 is typically used in deviceNET applications which allows for cable lengths of up to 100m at 500kbps.
It would be good if AD added next function in your CAN's chips:
The CAN transceivers provide a dominant timeout function that prevents erroneous CAN controllers from clamping the bus to a dominant level if the TXD input is held low for greater than 1ms.
This feature need for redundant control system
Thank you for the input. We will definitely consider this for future parts.
In the application note AN-770 the max. length is given with 40m - why is there a difference for the ADM3053 (25m to 40m) - can you explain?
40m for 1MHz
I couldn't find mentioning about 25m to 40m in ADM3053 datasheets or I have the old datasheets
The data-rate and cable length I mentioned was only examples of applications where it gets used. CANOpen is specified for 25m at 1Mbps.
Both the ADM3053 and ADM3052 have the same CAN transceiver and is capable of driving a 40m cable at 1Mbps.
How do you calculate this ?
Can you explain ?
The timing parameters are critical to setup correctly in the CAN controller when working at higher data rates.Example calculation:Bit Rate = 1MbpsCable length = 40mCable propagation delay = 5ns/mPropagation delay for physical layer transceiver = 250nsCAN controller oscillator frequency = 36MHzPhysical delay of cable = 5 x 40 = 200nstPROP_SEG = 2x(200 + 250) = 900nsA prescaler value of 1 gives a CAN system clock of 36MHz anda Time Quantum of 28ns. This will give 1000 / 28 = 36 time quanta per bit.PROP_SEG = ROUND_UP 900ns/28ns = 33From 36 time quanta per bit, subtract 33 for PROP_SEG and 1 for SYNC_SEG. This leaves 2 which is less than the absolute minimum required for PHASE_SEG1 and PHASE_SEG2.This will require an increase in the oscillator frequency from 36MHz:Physical delay of cable = 5 x 40 = 200nstPROP_SEG = 2x(200 + 250) = 900nsA prescaler value of 1 gives a CAN system clock of 40MHz anda Time Quantum of 25ns. This will give 1000 / 25 = 40 time quanta per bit.PROP_SEG = ROUND_UP 900ns/25ns = 36From 40 time quanta per bit, subtract 36 for PROP_SEG and 1 for SYNC_SEG. This leaves 3 which is the absolute minimum required for PHASE_SEG1 and PHASE_SEG2.PHASE_SEG1 = 1 Time QuantumPHASE_SEG2 = 2 Time QuantumDetermine RJW:RJW is chosen as the smaller of 4 and PHASE_SEG1. Oscillator tolerance:Deltaf < 1/(20x1000) = 0.005%Deltaf < 1/2(13x1000 – 2) = 0.0038%Best Regards,Hein
Message was edited by: Hein Marais
Can I use this isolator for automotive applications? Nothing specified in the datasheet!
Unfortunately the ADM3053 will not be qualified for automotive use.
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